Bazaar-NG vs. Mercurial -- speed comparison

[John Arbash Meinel]

Bryan O'Sullivan wrote:
> On 5/18/06, Aaron Bentley <aaron.bentley at utoronto.ca> wrote:
> 
>> Sure, but more data can also mean less reading at other points.  For
>> example, if knits didn't have snapshots, they'd have less data and more
>> reading would be required to construct an individual version.
> 
> Right. This is the tradeoff we make, too. For example, we have
> snapshots, as already mentioned. But in addition, we store a diff as a
> diff against the tip revision of a file, not against its parent
> revision. This usually makes the diff bigger, but we don't have to
> seek back to the parent in order to reconstruct that part of the file.
> We trade off file size against seek probability there, which has
> proven to be a win for performance. Diffing against the parent had a
> noticeable penalty for us when Chris Mason measured it.

Because we are doing annotations, we probably cannot do it that way. We
need to know what lines were introduced by this change versus its
parent, not just what lines exist.
You could probably do this after-the-fact by comparing the full-text of
the child against its parent. But there are some complications when you
have more than one parent (after a merge), and some of the parent lines
came from an even older ancestor.

Interesting to know, though.

John
=:->


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